Climate warming leads to changes in river ice across the Yukon Territory

There is a long-standing tradition where locals bet on the timing of ice break-up on the Yukon River in Dawson, Yukon. On April 23, 2016 at 11:15 am, a new record was set for the earliest break-up, shattering the previous record by four days since records started in 1896. The ice thickness on the Yukon River was below normal due to a record breaking warm winter, and warmer temperatures in early April produced a slow snowmelt that allowed water levels to slowly rise when the ice was relatively weak.

The timing of the river ice break-up of the Yukon River at Dawson, Yukon, has advanced significantly since 1896 at a rate of six days per century.

This record breaking timing of river ice break-up doesn’t come as a huge surprise. Since the mid-20th century, Canada’s North has warmed substantially. Annual temperatures have increased 2 to 3˚C between 1950 and 2012 in the northern region of Canada with more substantial warming occurring in the winter months (up to 6.5˚C). This warming has resulted in many widespread changes, including shorter and warmer winter seasons, earlier and more rapid snowmelt and changes in streamflow characteristics.

To better understand the impacts of a warming climate on cold regions, a Canadian interdisciplinary research network, the Changing Cold Regions Network (CCRN), was created in 2013 with funding from the Natural Sciences and Engineering Research Council of Canada (NSERC). Comprised of a team of over 40 researchers from across Canada, CCRN aims to understand, diagnose and predict the rapid environmental change in the interior of Western Canada, including Canada’s North.

Richard Janowicz, Senior Scientist, Hydrology for the Water Resources Branch at Yukon Environment, is a scientific collaborator with CCRN and has been studying streamflow in the Yukon Territory for decades. His research has shown that streamflow characteristics have been changing over the last century, yet those changes seem to have been accelerated in the last two decades.

“Prior to 1989, only two April break-ups have been observed on the Yukon River at Dawson, whereas after 1989, eight April break-ups have been observed,” including 2016. Janowicz’s research has shown that river ice break-up at Dawson has advanced at a rate of six days per century and similar trends have been observed on other Yukon rivers, including the Porcupine River at Old Crow. “Over the last two decades, the duration of ice cover on the Yukon River has been declining at a faster rate than during the 21st century.”

Streamflow hydrographs from Porcupine Creek at Old Crow, Yukon.Warmer spring temperatures have caused a merging of river ice break-up and snowmelt freshet.

Spring temperatures have increased 2 to 4˚C since 1950, which has been one of the drivers behind the earlier onset of snowmelt and river ice break-up. The timing of snowmelt has changed more rapidly than river ice break-up. The duration of snow cover in spring has declined by approximately one month since 1972 across much of the Yukon Territory. Such a change in snowmelt timing has resulted in the merging of the normally distinct river ice break-up and snowmelt events, forming one main spring streamflow peak, Janowicz explains. Historically, Porcupine River streamflow has two distinct peaks in spring — the first peak is caused by river ice break-up and jamming and the second peak is driven by the snowmelt freshet that normally follows one to three weeks later. More recently, those two peaks have merged into one, forming a larger peak in spring streamflow.

“Frozen rivers are a means of transportation for many locals as well as a platform for fishing and trapping purposes. Such changes in river ice presents a unique challenge and even threatens the livelihood of some communities.” With temperatures still on the rise across much of Northern Canada, the river ice regimes will continue to see rapid changes.

To learn more about this and other environmental impacts due to climate warming across Western and Northern Canada, visit CCRN’s website at www.ccrnetwork.ca.